This application claims the priority of German Application No. 197 25 010.6, filed Jun. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement having an electromagnetic actuator for actuating a charge cycle valve.
Electromagnetic actuators for actuating charge cycle valves of an internal-combustion engine, as a rule, have two switching magnets--an opening magnet and a closing magnet--between whose pole faces an armature is arranged so that it can be displaced coaxially with respect to a valve shaft of the charge cycle valve. The armature acts directly or by way of a tappet upon a valve stem of the charge cycle valve. In the case of actuators according to the principle of a mass oscillator, a prestressed spring mechanism with two prestressed pressure springs acts upon the armature or the armature tappet, specifically an upper and a lower valve spring. If both valve springs are arranged below the actuator, as a rule, the upper valve spring is supported in the direction of the actuator on the opening magnet and is supported in the direction of the charge cycle valve on a spring plate fixedly connected with the armature tappet, and acts in the opening direction of the charge cycle valve. The lower valve spring is supported in the direction of the charge cycle valve on a cylinder head and is supported in the direction of the actuator on a second spring plate fixedly connected with the valve stem, and acts in the closing direction of the charge cycle valve. When the magnet is not energized, the armature is held in a condition of equilibrium between the magnets by means of the valve springs.
When the actuator is operated, the closing magnet or the opening magnet is overexcited for a short time or the armature is caused to carry out oscillations by means of a stimulating routine in order to attract it out of the condition of equilibrium. In the closed position of the charge cycle valve, the armature will rest against the pole face of the energized closing magnet and is held by it. The closing magnet prestresses the valve spring acting in the opening direction. In order to open the charge cycle valve, the closing magnet is switched off and the opening magnet is switched on. The valve spring acting in the opening direction accelerates the armature beyond the condition of equilibrium so that it is attracted by the opening magnet. The armature strikes against the pole face of the opening magnet and is held by it. In order to close the charge cycle valve again, the opening magnet is switched off and the closing magnet is switched on. The valve spring operating in the closing direction accelerates the armature beyond the condition of equilibrium to the closing magnet. The armature is attracted by the closing magnet, strikes on the pole face of the closing magnet, and is held by it.
From an older application--German Patent Document DE 197 07 810.9 (corresponding to U.S. Ser. No. 09/031,741, filed Feb. 27, 1998, and commonly owned by the assignee of the present invention, the specification of which is expressly incorporated by reference herein) a spring mechanism is known which has only one spring. The spring is arranged in a prestressed manner on the valve stem below the opening magnet between an upper driving element facing away from the charge cycle valve and a lower driving element facing the charge cycle valve. A spring plate is arranged in each case between the driving element and the spring, which spring plates are guided coaxially displaceably with respect to one another on the driving elements. During the closing and opening of the charge cycle valve, the spring is moved between an upper and a lower path boundary. In the case of an approximately central position, the spring is supported on the two path boundaries. When the charge cycle valve is opened from the central position, the lower driving element dips into the lower path boundary. The spring is then supported in the downward direction by way of the lower spring plate on the lower path boundary and is supported in the upward direction by way of the upper spring plate on the upper driving element, by which it is prestressed further. When the charge cycle valve is closed from the central position, the upper driving element dips into the upper path boundary, the spring is supported by way of the upper spring plate on the upper path boundary and is supported by means of the lower spring plate on the lower driving element, which prestresses the spring.
If the same distance exists between the driving elements as between the path boundaries, an arrangement is achieved which has no play and in which the central position of the armature is determined precisely by the spacing, independently of a spring rate. In addition, the expenditures of the spring system are reduced in that only one spring is required which, because of a lower required prestressing, can be dimensioned to be weaker and smaller. Specifically, the described spring deflection system is particularly short because only one spring is required which, in addition, is prestressed further by the driving elements only by half the lift course of the charge cycle valve.
The described advantages of the spring deflection system contrast with a relatively high-expenditure mounting, during which first the valve stem must be inserted from below into the cylinder head and subsequently the parts of the actuator must individually be pushed onto the valve stem and then be positioned and fastened, such as the lower driving element, the lower spring plate, the spring, the upper spring plate, the upper driving element, the closing magnet and the armature.
It is an object of the present invention to permit a simple mounting, while simultaneously improving the operation of the actuator.
According to the present invention, this object is achieved by an arrangement for actuating a charge cycle valve having an electromagnetic actuator which has an opening magnet and a closing magnet between which an armature is arranged in a coaxially displaceable manner. The armature acts upon a valve stem. A spring acts upon the valve stem and is arranged between an upper driving element facing away from the charge cycle valve and a lower driving element facing the charge cycle valve. The elements are connected for the joint movement with the armature. The spring is displaceable between an upper path boundary and a lower path boundary and is supported in the opening position of the charge cycle valve in the upward direction on the upper driving element and in the downward direction on the lower path boundary, in the closing position of the charge cycle valve the spring is supported in the upward direction on the upper path boundary and in the downward direction on the lower driving element. The armature has an armature tappet which is connected by way of a connection element with the valve stem.
The invention is based on the recognition that a mounting of the component parts of the actuator directly on a cylinder head, that is, the individual pushing-on, positioning and fastening of the parts on a valve stem already inserted in the cylinder head is difficult and is associated with high expenditures, particularly because of the narrow space conditions which exist. It is advantageous for the actuator to be preassembled separately in sufficient space and to be mounted on the cylinder head in the preassembled condition. This is permitted by means of the actuator according to the present invention whose armature has an armature tappet which is separate from the valve stem. The armature tappet is connected with the valve stem by way of a connection element, for example, by means of a clamped, screwed, welded or other suitable form-locking, force-locking or substance-locking connection.
In addition to being mounted in a favorable manner, the preassembled actuator can be tested separately before the installation on the cylinder head. The central position is determined by the position of the driving elements and of the path boundaries. It does not depend on a spring rate and thus, particularly, also not on a second lower valve spring which, in the case of known actuators, would not be preassembled and would therefore have to be simulated in the case of a preliminary test. As a result, fault sources, such as deviating spring rates of the lower valve spring, cannot be taken into account during the test. Tolerances caused by a second valve spring are avoided.
In this context, it is particularly advantageous for both driving elements to be fastened on the armature tappet. The spring is arranged on the armature tappet so that it cannot be lost and the positions of the driving elements can be tested beforehand.
In a further development of the invention, both path boundaries are fixedly connected with the actuator or are formed by it, whereby these can also be preassembled. If, in addition, the connection element is preassembled on the armature tappet, all component parts of the actuator are now defined beforehand and can be tested with respect to their position and operation. Faults can be recognized early and at low cost, and the consequences of faults can be limited to a minimum.
Additional details of the invention as well as resulting advantages are indicated in the following description of embodiments.
In the description and in the claims numerous characteristics are illustrated and described within the context. A person skilled in the art will expediently also consider the characteristics separately and assemble them to form additional suitable combinations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.